I agree with you about the lighting, but this is an area where I never expected PJ to use the kind of approach that I prefer, since it's not his style, so it doesn't really disappoint me. I expect the main strength of "Riddles in the dark" to be in characterization and the interaction between Bilbo and Gollum and a progression from slight comedy to something more menacing and sinister. I also expect the use of music to be more prominent than the use of visual measures. If Jackson actually has decided to put more emphasis on atmosphere through visual cues, I will be pleasantly surprised.

The choice of brighter colours was made from the start I believe and seems to be something Del Toro and Jackson agreed upon as a way of differentiating The Hobbit from LoTR. How the tone of the story affects the rest of the visuals in the films remains to be seen (like you also note in your last paragraph).